Nuclear magnetic resonance T1 relaxation time definition

Hi all:
I have one confused concept about T1 relaxation time in nuclear magnetic resonance field.
As we know, fluctuation of local magnetic field inside the sample causes T1 decay in the following RF excitation. Imagine one simple mode, near a gadolinium ion (Gd3+), there is one water molecule. For ideal case, there are no other atom or molecule. The whole system consists of the ion and single water molecule. We know total magnetic moment is fixed for Gd3+. Total magnetic moment include spin magnetic moment, spin-orbital magnetic moment, electron orbital magnetic moment, and ion rotation induced magnetic moment, et al. If total magnetic moment is contant, how can this ion generate a fluctuation of magnetic field in the site of water molecule? thanks

Staff: Mentor

Mostly by thermal motion closer to or further from the water molecule. As the distance between the two changes the water molecule's local magnetic environment changes and the water becomes more likely to exchange energy with the lattice.

Mostly by thermal motion closer to or further from the water molecule. As the distance between the two changes the water molecule's local magnetic environment changes and the water becomes more likely to exchange energy with the lattice.

Thanks for your advice and answer. I found one possible answer. The only reason to make Gd3+ ion change its total magnetic moment is due to collision of inter-molecule(diffusion). You can imagine that in water solution, the average distance between two water molecules are 3x10^-10 meter. Violent frequent collision keep changing the direction of total magnetic moment. Now fluctuation of local magnetic field cause T1 decay. thanks again